I realize you are a civil engineer. That's why I figured you'd be a bit more educated on the subject.
If towns, villages, cities, and the state didn't think that these bike paths or rail trails were of importance to them, they wouldn't spend the time to either gravel or pave them. These aren't political statements to be green, nobody commutes on a rail trail, it's a tourist trap. It's a way to generate recreational revenue. You want to tax beach users too?
As for city installed cycle paths for commuters these again are for weekend recreational users and weekly commuters, paid for by property taxes.
You want to tax me for owning a bike? Sure, I'll pay taxes for owning a bike, just as soon as you are taxed for your guns, four wheelers, jeeps, fishing poles, bow, hockey sticks (imagine all the emissions an ice rink puts out trying to keep the ice frozen), chainsaw, etc.
You try to force people to find a greener alternative to the car to commute, then try to force a tax on it?
Or on the flip side are you ok with taxing recreation? I pay for access to the trails I ride just the same as an ORV user or Snowmobile does. I either have to purchase a daily pass to the state parks, a yearly pass, or the same for a private park, city park, county park......